A projection lamp unit which forms part of a projection system such as mentioned above generally includes a preformed glass reflector and projection lamp (e.g. tungsten halogen). The reflector generally has an elliptical surface of revolution with the lamp filament at or near the focal point for concentrating a beam of light through the system's various elements (e.g. film gate and associated lens). Examples of such lamp units are found in U.S. Pat. Nos. 3,789,212 and 3,761,170. In some units, the reflector surface is smooth and highly polished (specular) so as to maximize the controlled energy directed through the system. The aforementioned U.S. Pat. Nos. 3,761,170 and 4,392,189 illustrate such a smooth surfaced reflector.
Although the smooth and highly polished reflector provides substantially maximum optical output, the resulting beam pattern often tends to be non-uniform, creating what are termed "hot spots" and thus resulting in degraded resolution of the projected image. In view of such non-uniformity of the beam pattern, many present designs utilize a reflector surface that is completely diffuse (e.g., containing peens or facets). In this regard, see U.S. Pat. Nos. 3,825,742, 4,035,631 and 4,021,659, as well as British patent application No. 2,085,745A. U.S. Pat. No. 4,021,659 in particular illustrates an all-faceted projection lamp unit reflector presently employed in some commercial projecting units.
Although the totally faceted reflector improves the uniformity of the beam pattern in comparison to all-specular surfaced reflectors, there tends to be a significant light loss using such a surface.